Hidden Galaxies Detected

Hidden Galaxies Detected
Artist's impression showing how a background quasar can hide a galaxy. The light that travels from the quasar is filtered by the foreground galaxy on its way to Earth.
(Image: © European Southern Observatory)

Deer can'tsee cars at night because of blindingly bright headlights. And until now,astronomers couldn't see foreground galaxies outshined by the dazzling quasarsbehind them.

A new techniquecan pick apart the intense pattern of light emitted by quasars, findingirregularities in the image where "invisible" galaxies are absorbingsome of the quasar light.

"Thedifficulty in actually spotting and seeing these galaxies stems from the factthat the glare of the quasar is too strong compared to the dim light of thegalaxy," said Nicholas Bouche, an astronomer at the Max Planck Institutefor Extraterrestrial Physics in Munich, Germany.

Bouche andhis team's findings will be detailed in an upcoming issue of AstrophysicalJournal.

Verylarge help

Quasars aresmall, distant and extremely bright cosmicbeacons that produce more light than typically comes from an entire largegalaxy. In spite of their brightness, however, some of the light is soaked upby intervening objects during its long journey to Earth's telescopes.

To locatethe so-called "invisible" galaxies, Bouche and his team lookedthrough huge catalogues of quasar data and picked out those with"dips" in their light signatures. Then, using the European SouthernObservatory's (ESO) Very Large Telescope (VLT), located in the mountains ofnorthern Chile, the team searched for galaxies close to the pulse of quasarlight.

Theastronomers capitalized on the VLT's special infrared spectrometer, calledSINFONI, to pick apart 20 patches of sky around the quasars to search forgalaxies from the time when the universe was about 6 billion years old, almosthalf its current age. Seventy percent of the time, they found a galaxy hidingin the "headlights"of a quasar.

So far, theastronomers who pioneered the technique have detected 14 hidden galaxies bytargeting the VLT on unusual quasar light signatures.

Galaxyhunt

Bouche saidhe is surprised by not only the amount of galaxies he and his colleagues havefound hiding near quasars,but also by the types of these galaxies.

"Theseare not just ordinary galaxies," he said. "They are ? activelyforming a lot of new stars and qualifying as 'starburst galaxies.'"

These typesof galaxies are forming the equivalent of about "20 suns per year,"noted team member Celine Peroux, an astronomer at the Institute of Astronomy in Cambridge.

The teamthinks their finding will spur a new hunt for galaxies in the universe.

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